Downhole Tool

ABSTRACT

A method and apparatus for a downhole tool including a slip assembly having a plurality of slips configured to engage a downhole surface. The slip assembly includes a plurality of slip segments. Each slip segment includes a slip body, a plurality of profile elements coupled to the slip body, and a first coating disposed on the plurality of profile elements, wherein the first coating is formed from a plasma electrolytic oxidation treatment. The first coating and the plurality of profile elements form a plurality of gripping elements configured to grip the downhole surface.

BACKGROUND Field

Embodiments of the present disclosure generally relate to a downholetool including a coating, wherein the coating is formed using a PlasmaElectrolytic Oxidation (“PEO”) process.

Description of the Related Art

Slips are used for various downhole tools, such as bridge plugs andpackers. The slips may include buttons (e.g., gripping inserts)configured to grip the inner wall of a casing or tubular. Buttons may bemade from cast or forged metal, which may then be machined andheat-treated to the proper engineering specifications according toconventional practices.

Some conventional slip assemblies are coated with a sprayed-on hardfacing, which may have poor adhesion to the slips and may provideineffective corrosion resistance or provides a poor barrier between theslip and wellbore fluids. Conventional slip assemblies may also havenon-dissolvable buttons that are used to grip (e.g. bite) into adownhole tubular. If these buttons are attached to a dissolvable slip,the slip may dissolve in the presence of a chemical solution whileleaving behind the buttons. The buttons might release from engagementwith a downhole tubular after the dissolution of the slips. The buttonsmay impede subsequent downhole operations. As a result, a cleaningoperation may be necessitated to flush the buttons back to the surface.

There is a need in the art for a slip with a coating that is welladhered to the slip, resistant to corrosion, and provides a barrierbetween portions of the slip and the wellbore fluids. There is also aneed in the art for a sufficiently hard coating that can be applied on aslip to cover dissolvable gripping elements such that the coatingcontacts the downhole tubular to anchor a downhole tool.

Conventional seats of downhole tools may be damaged by the flow ofwellbore fluids through the downhole tool such that an object cannotproperly engage the seat. For example, a fracturing fluid including sandand/or proppants may damage the seat, preventing an object from creatinga sealing engagement with the seat. For example, the seat may be damagedby corrosion caused by the wellbore fluids. There is a need in the artfor a downhole tool with a seat including a damage resistant coatingsuch that an object can sealing engage with the seat.

SUMMARY

In one embodiment, a downhole tool includes a cone member and a slipassembly. The slip assembly includes a plurality of slip segments. Theslip segments are configured to move along the cone member intoengagement with a downhole surface. Each slip segment includes a slipbody, a plurality of degradable profile elements coupled to the slipbody, and a first coating disposed on the plurality of profile elements,wherein the first coating is formed from a plasma electrolytic oxidationtreatment. The first coating and profile elements form a plurality ofgripping elements configured to grip the downhole tubular.

In one embodiment, a downhole tool includes a slip assembly having aplurality of slips configured to engage a downhole surface. The slipassembly includes a plurality of slip segments. Each slip segmentincludes a slip body, a plurality of profile elements coupled to theslip body, and a first coating disposed on the plurality of profileelements, wherein the first coating is formed from a plasma electrolyticoxidation treatment. The first coating and the plurality of profileelements form a plurality of gripping elements configured to grip thedownhole surface.

In one embodiment, a method of using a downhole tool includes deployinga downhole tool into a downhole tubular. The downhole tool includes aslip assembly. The slip assembly includes a plurality of slip segmentshaving a coating formed from a plasma electrolytic oxidation treatment,wherein the coating is configured to grip the downhole tubular. Themethod further includes activating the downhole tool to engage theplurality of slip segments with the downhole tubular, wherein thecoating grips the downhole tubular such that the slip assembly anchorsthe downhole tool to the downhole tubular.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlyexemplary embodiments and are therefore not to be considered limiting ofits scope, may admit to other equally effective embodiments.

FIG. 1 illustrates an exemplary embodiment of a downhole tool.

FIG. 2 illustrates a cross-sectional view of the downhole tool show inFIG. 1.

FIG. 3A illustrates an exemplary slip segment. FIG. 3B illustrates across-sectional view of the slip segment shown in FIG. 3A. FIG. 3Cillustrates the circled region in FIG. 3B.

FIG. 4 illustrates a cross-sectional view of an alternative embodimentof a slip segment.

FIG. 5 illustrates a flow diagram of a method for a PEO treatment todevelop a PEO coating.

FIG. 6 illustrates a cross-sectional view of the downhole tool of FIG. 1with slips engaged with a downhole tubular.

FIG. 7 illustrates a cross-sectional view of an exemplary downhole toolincluding a seat having a PEO coating.

FIG. 8 illustrates a cross-sectional view of an exemplary downhole toolincluding multiple seats having a PEO coating.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary downhole tool 100 according to anembodiment of this disclosure. The downhole tool 100 may be a bridgeplug as shown, but it could also be a packer, a liner hanger, ananchoring device, or other downhole tool that uses a slip assembly toengage a downhole surface, such as a casing.

The downhole tool 100 includes a mandrel 110, a slip assembly 120, acone 140, a shoe member 150, and a seal assembly 160. As shown, the slipassembly 120 is disposed between the cone 140 and the shoe member 150.The slip assembly 120 may include a plurality of slip segments 122. Theseal assembly 160 may include one or more seal segments 162. One end ofthe mandrel 110 (FIG. 2) is releasably attached to the shoe member 150.For example, a shear ring 152 is used to releasably attach the mandrel110 and the shoe member 150. The shear ring 152 can be disposed betweenthe mandrel 110 and a nut 114 coupled to the end of the mandrel 110. Oneor more bands 123 may be used to retain the seal segments 162 and slipsegments 122 on the downhole tool 100. In some embodiments, the bands123 are expandable. FIG. 1 illustrates the downhole tool 100 coupled toa setting sleeve 113 for activating the downhole tool 100.

FIG. 2 illustrates a cross-section of FIG. 1. The cone 140 includes aninclined surface and is arranged on the mandrel 110 with its inclinedsurface facing the shoe member 150. In this example, teeth 143 areformed on the inclined surface of the cone 140 for mating with the teethof the sealing assembly 160 and the teeth 133 of the slip assembly 120.As shown, the mandrel 110 is disposed within the slip assembly 120, thecone 140, the shoe member 150, and the seal assembly 160.

FIG. 3A illustrates an exemplary slip segment 122. The slip segment 122includes a slip body 130 and a slip insert 125. The slip body 130 has aninclined surface 132 for riding on the inclined surface of the cone 140.Teeth 133 may be provided on the inclined surface 132 for mating withthe teeth 143 of the cone 140. The slip body 130 may have grooves 131corresponding to the bands 123. The end of the slip body 130 with theinclined surface has a wedge shape. One or more sealing protrusions 135having an arcuate shape are formed on the outer surface of the wedgeshaped end of the slip body 130. The slip insert 125 includes one ormore gripping elements 126 composed of a profile element 128 coated witha PEO coating 129. The surface of the PEO coating 129 in FIG. 1 throughFIGS. 3A-3B is shown with a shading.

In one embodiment, the slip body 130 is made of a dissolvablenon-metallic material. Suitable dissolvable non-metallic materialsinclude dissolvable non-metallic polylactic acid (PLA) based polymers,polyglycolic acid (PGA) based polymers, degradable urethane, and otherpolymers that are dissolvable over time. In one example, the slip body130 is manufactured using an injection molding process. The dissolvablenon-metallic material is injected into a mold of the shape of the slipbody 130, where it is allowed to solidify before removal from the mold.The injection molding process advantageously provides for a lower costslip assembly manufacturing process and for various designs of the slipassembly 120 such as segmented, interconnected, or unitary body. In someembodiments, the slip body 130 is formed from a dissolvable metallicmaterial, such as an aluminum or magnesium alloy. In one embodiment, thebands 123 may be made of a dissolvable non-metallic material or adissolvable metallic alloy.

As shown in FIGS. 3A and 3B, the slip insert 125 is disposed in a pocket136 formed in the slip body 130. Each slip insert 125 includes a body127 and one or more profile elements 128. The profile elements 128 maybe attached to or integral with the body 127 of the slip insert 125. Forexample, the profile elements 128 may be a plurality of wickersintegrally formed with the body 127 as shown in FIGS. 3A-3B. The slipinsert 125 may be machined to form the profile elements 128. In someembodiments, the profile elements 128 may include one or moredissolvable and/or non-dissolvable buttons attached to the body 127. Insome embodiments, the entire slip insert 125 and profile elements 128are made of a degradable metallic material such as a dissolvablemetallic material. Suitable dissolvable metallic materials includemagnesium alloys or aluminum alloys. In some embodiments, the aluminumalloy may be about 75% to about 95% aluminum. In some embodiments, themagnesium alloy may be about 75% to about 95% magnesium. In someembodiments, the aluminum alloy may include magnesium. In someembodiments, the magnesium alloy may include aluminum. The dissolvablemetallic materials begin to dissolve upon interaction with a chemicalsolution, such as a solvent. The solvent may be an electrolyte solution.In some embodiments, the cone 140 may be made from an aluminum ormagnesium based alloy.

In one embodiment, one or more components of the downhole tool 100 arepreferably composed of degradable materials, such as dissolvablematerials, so the downhole tool 100 can be removed from the wellboreupon completion of operations without requiring a drilling-outoperation. For example, at least one of the slip assembly 120, the cone140, the shoe member 150, and the seal assembly 160 can be manufacturedfrom a degradable material. In one example, the cone 140 may be made ofa degradable polymer. In one example, one or more components of thedownhole tool 100 are composed of a dissolvable material. An exemplarydissolvable material is a dissolvable polymeric material.

In some embodiments, one or components of the downhole tool 100 may beformed from a degradable material, such as a dissolvable metallicmaterial, that is reactive with a chemical solution that is anelectrolyte solution. The electrolyte solution to degrade the downholetool 100 may include an electrolyte selected from the group comprising,consisting of, or consisting essentially of solutions of an acid, abase, a salt, and combinations thereof. A salt can be dissolved inwater, for example, to create a salt solution. Common free ions in anelectrolyte include, but are not limited to, sodium (Na⁺), potassium(K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), chloride (Cl⁻), bromide (B⁻)hydrogen phosphate (HPO₄ ²⁻), hydrogen carbonate (HCO₃ ⁻), and anycombination thereof. Preferably, the electrolyte contains halide ionssuch as chloride ions.

The profile elements 128 are coated with the PEO coating 129 to form thegripping elements 126. The gripping elements 126 are configured to grip(e.g., bite) a downhole surface, such as the surface of a downholetubular or the surface of the wellbore, when the slip assembly 120 is ina radially extended position. For example, when the gripping elements126 grip the downhole surface, the downhole tool 100 is anchored in thedownhole surface. The downhole surface may be a casing. In someembodiments, the PEO coating 129 is formed on and bonded to the uppersurface of the body 127 and the profile elements 128. Thus, the insert125 includes the PEO coating 129. In some embodiments, the profileelements 128 are spaced apart from one another and the PEO coating 129is formed on and bonded to only the profile elements 128 while theremainder of the upper surface of the body 127 is not coated, leaving anuncoated surface between adjacent coated profile elements 128.

As shown in FIGS. 3A and 3B, the upper surface of the body 127 isdefined by the profile elements 128, which are shown as wickers. FIG. 3Cillustrates the circled region in FIG. 3B to better show the coating 129on the profile elements 128. The profile elements 128 are coated withthe PEO coating 129. The PEO coating 129 is formed on and bonded to theprofile elements 128. As shown in FIGS. 3B and 3C, the PEO coating 129has a cross-section that follows the cross-section of the profileelements 128. As a result, the outer surface of the PEO coating 129reflects a shape similar to the shape of the profile elements 128. As aresult, the gripping elements 126 reflect the shape of the profileelements 128. As shown in FIGS. 3A-3B, the gripping elements 126 reflectthe shape of the wickers 128 and are thus generally wicker shaped. Theone or more gripping elements 126 form a gripping surface of the slipinsert 125 that engages and/or bites into the downhole surface.

As shown in FIG. 3B, the slip insert 125 may include one or more tongues137 that are engageable with one or more slots formed in the slip body130. The tongues 137 facilitate attachment of the slip insert 125 to theslip body 130.

In one embodiment, the slip insert 125 is attached to the slip body 130after the slip body 130 is removed from an injection mold. In anotherembodiment, the slip insert 125 is disposed in an injection mold beforethe slip body 130 material is injected into the mold. In this respect,the slip insert 125 is attached to the slip body 130 as the slip body130 solidifies.

In some embodiments, the slip insert 125 undergoes a PEO treatment suchthat the slip insert 125 includes the PEO coating 129 before attachingthe slip insert 125 to the slip body 130. In some embodiments, the slipinsert 125 and the slip body 130 undergo a PEO treatment together, suchas when the slip insert 125 is integral to the slip body 130. In someembodiments, the PEO coating 129 may have a thickness of about 20microns to about 250 microns. For example, the PEO coating 129 may beabout 40 microns thick. In some embodiments, the PEO coating 129 has ahardness of about 300 Vickers to about 2000 Vickers, such as about 1500Vickers to about 2000 Vickers. For comparison, the hardness of aconventional steel casing is about 350 Vickers to about 400 Vickers. Insome embodiments, the slip insert 125 is treated such that the entiresurface of the slip insert 125 includes the PEO coating 129. In someembodiments, only the upper surface of the body 127 with the profileelements 128 is treated to include the PEO coating 129. In someembodiments, surfaces can be masked to avoid being treated to preventthe application of a PEO coating. For example, the non-coated areas maybe masked with an inert material prior to the PEO treatment. The PEOcoating 129 is bonded with the slip insert 125, such as the profileelement 128. Because PEO coating 129 forms the outer surface of thegripping elements 126, the PEO coating contacts and/or penetrates thedownhole surface when the slip segments 122 are set. In addition to thehigh hardness properties, the PEO coating 129 has a low stiffness whichenables the PEO coating 129 to withstand strains, such as thermallyinduced strains associated with wellbore temperatures, withoutde-bonding from the underlying slip insert 125, such as de-bonding fromthe profile elements 128. Additionally, the PEO coating 129 prevents thecoated surface, such as the surface of the profile elements 128 and/orthe upper surface of the body 127, from being in contact with wellborefluids.

In some embodiments, a chemical solution may be flowed downhole todegrade the slip insert 125. The chemical solution may interact with thenon-coated areas, resulting in the degradation of the slip insert 125.For example, the slip body 130 and slip insert 125 may be sufficientlydegraded such that portions of the downhole tool 100 may be flushed fromthe wellbore. In some embodiments, the PEO coating 129 remains and isnot chemically reactive with the chemical solution. The PEO coating 129may remain engaged with the downhole surface or it may be flushed fromthe wellbore. Without being bound by theory, it is believed that thethin PEO coating 129 may break up into smaller pieces due to the flow ofwellbore fluids once the slip insert 125 is degraded and no longersupports the PEO coating 129 against the downhole surface.

When deployed downhole, the downhole tool 100 is activated by a settingtool, such as a wireline setting tool, which uses conventionaltechniques of pulling the mandrel 110 while simultaneously pulling theslip assembly 120 against the cone 140. The cone 140 is axially abuttedagainst the setting sleeve 113. As a result, the slip assembly 120 ridesup the cone 140 and move from the radially retracted position to theradially extended position to engage a downhole surface, such a wall ofthe surrounding downhole tubular or the surface of the wellbore. Thegripping elements 126 grip the downhole surface when the slip assembly120 is in the radially extended position. The individual slip segments122 are prevented from riding back down the cone 140 by the engagementof the teeth 133 of the slip segments 122 and the teeth 143 of the cone140. The slip segments 122 may be fully or partially wedged between thecone 140 and the downhole surface. In this manner, the slip assembly 120retains (e.g., anchors) the downhole tool 100 in place. The slipassembly 120 also causes the seal assembly 160 to move up the inclinedsurface of the cone 140. The individual seal segments 162 move intoengagement with the downhole surface. For example, the seal segments 162include one or more sealing protrusion 165 configured to engage thedownhole surface. The slip segments 122 further include one or moresealing protrusions 135 configured to engage the downhole surface. Whenthe downhole tool 100 is activated, and the slip assembly 120 and theseal assembly 160 are set, the sealing protrusions 165 of the sealsegments 162 are configured to form a seal ring with the sealingprotrusions 135 of the slip segments 122. This seal ring seals theannulus between the downhole tool 100 and the downhole surface. Once thedownhole tool 100 is activated, the setting sleeve 113 and mandrel maybe retrieved to the surface.

To begin a fracturing operation, an object, such as a ball or a dart, isreleased into the wellbore and lands in a seat 142 of the downhole tool100. The seat 142 may be formed in the interior of the cone 140.Fracturing fluid is pumped into the wellbore to fracture the formationupstream from the downhole tool 100 with the seated object. Afterpumping the fracturing fluid, the downhole tool 100 may degrade, such asdissolve, over time, thereby eliminating the need for a drilling-outoperation to remove the downhole tool 100. For example, one or morechemical solutions may be pumped downhole to degrade one or morecomponents of the downhole tool 100.

In some embodiments, the downhole tool 100 does not include a sealassembly 160 and the slip segments 122 do not have corresponding sealingprotrusions 135. In some embodiments, the downhole tool 100 includes analternative seal assembly that does not include seal segments. In someembodiments, the slip segments 122 do not include a wedged shape end,and the slip segments 122 is configured to move an alternative sealassembly, such as an elastomeric ring, along the inclined surface of thecone 140 such that the elastomeric ring expands into sealing engagementwith the downhole surface.

FIG. 4 illustrates a cross-sectional view of an alternative embodimentof the slip segment 122 a according to another embodiment of thedownhole tool 100. The slip segment 122 a includes a slip body 230, apocket 236, and a slip insert 225. The slip segment 122 a may furtherinclude grooves 231 corresponding to the bands 123. As shown, the slipinsert 225 has a first PEO coating 229 u and a second PEO coating 229 b.The first PEO coating 229 u and the second PEO coating 229 b may havethe same or substantially the same thickness and hardness values as thePEO coating 129. As shown, the slip segment 122 a does not include oneor more protrusions corresponding to a seal assembly 160. The slipsegments 122 a may be used with a downhole tool 100 that does notinclude a seal assembly 160, or the slip segments 122 a mayalternatively be used with an alternative seal assembly 160 that doesnot include a plurality of seal segments. In some embodiments, the slipsegments 122 a may include one or more sealing protrusions and thus thedownhole tool 100 can include both slip segments 122 a and the sealassembly 160 with the seal segments 162. In some embodiments, the slipsegments 122 a are used with a downhole tool with an alternative sealassembly that seals against a downhole surface that includes sealsegments 162. In some embodiments, the slip segments 122 a may be usedwith an alternative seal assembly that is an elastomer ring configuredto expand into a sealing engagement with the downhole surface as theelastomer ring travels along the inclined surface of the cone 140

The slip insert 225 is disposed in a pocket 236. The slip insert 225includes a body 227. The pocket 236 extends through the depth of theslip body 230. The slip insert 225 includes an upper surface configuredto face the downhole surface and a lower surface opposite the uppersurface and configured to face the cone 140. Each slip insert 225includes one or more first profile elements 228. The first profileelements 228 may be attached to or integral with the upper surface ofthe body 227. The first profile elements 228 coated with the first PEOcoating 229 u form the one or more gripping elements 226. The one ormore gripping elements 226 are configured to grip (e.g., bite) thedownhole surface when the slip segments 122 a are set. The one or moregripping elements 226 form a gripping surface of the slip insert 225that engages and/or bites into the downhole surface. An uncoated areamay be between adjacent, but spaced apart, profile elements 228.

In some embodiments, the first profile elements 228 may be wickersintegral with the body 227 as shown in FIG. 4. In some embodiments, thefirst profile elements 228 may be one or more degradable buttons, suchdissolvable buttons, attached the upper surface of the body 227. In someembodiments, the first profile elements 228 may be one or morenon-dissolvable buttons attached to the upper surface of the body 227.In some embodiments, the slip insert 225 and first profile elements 228are made of a dissolvable metallic material.

In some embodiments, and as shown in FIG. 4, the lower surface of theslip insert 225 includes teeth 234. The teeth 234 are configured toengage with teeth 143 of the cone 140. Each tooth 234 may be composed ofa second profile element 233 coated with the second PEO coating 229 b.In some embodiments, the slip insert 225 may be machined to form thefirst profile elements 228 and the second profile elements 233. The slipinsert 225 may have a tongue 237. Suitable dissolvable metallicmaterials include magnesium or aluminum based dissolvable alloys. In oneembodiment, the dissolvable metallic materials are dissolvable uponinteraction with chemical solution, such as an electrolyte solution.

In some embodiments, the slip body 230 includes an inclined surface 232corresponding to the inclined surface of the cone 140. In someembodiments, the slip insert 225 and/or the slip body 230 include theinclined surface 232. As shown, the teeth 234 are disposed on theinclined surface 232.

In some embodiments, the slip insert 225 is entirely coated with a PEOcoating 229. In some embodiments, only the upper surface and the firstprofile elements 228 are coated with the first PEO coating 229 u and theteeth 234 are simply the second profile elements 233 without a coating.In some embodiments, and as shown in FIG. 4, the upper surface of thebody 227 and first profile elements 228 are coated with the first PEOcoating 229 u and the lower surface and second profile elements 233 arecoated with the second PEO coating 229 b. The first PEO coating 229 u isbonded to the first profile elements 228 and has a cross-section thatfollows the cross section of the first profile elements 228. As aresult, the outer surface of the first PEO coating 229 u reflects ashape similar to the shape of the first profile elements 228. The secondPEO coating 229 b covers and is bonded to the second profile elements233. The second PEO coating 229 b has a cross section that follows thecross-section of the second profile elements 233. As a result, the outersurface of the second PEO coating 229 b reflects a shape similar to theshape of the second profile elements 233.

The slip segment 122 a may be formed in a similar manner as discussedabove with respect to slip segment 122.

FIG. 5 is a flow diagram of a method 300 for a PEO treatment to developa PEO coating. The method 300 begins at operation 301, in which surfacesof a substrate, such as the surface of the profile elements 128, 228,233, and/or the surface of the body 127, 227, are subjected to acleaning operation. In one example, the substrate may include analuminum alloy or a magnesium alloy. The operation 301 may includeexposure to one or more of a degreasing agent, an alkaline soak, and aclean water rinse to remove particulates or other debris from surfacesof the substrate where a PEO coating is desired. For example, the insert125, 225 may be cleaned in operation 301. In operation 302, a maskingmaterial may be applied to the substrate to mask areas in which theformation of a PEO coating undesired. For example, every surface of theslip insert 125 but the upper surface may be masked. In operation 303,the substrate and the optional masking are placed in an electrolyticbath. The electrolytic bath includes the materials necessary to form thePEO coating, such as PEO coating 129. The electrolyte material may beselected based on the desired PEO coating to be developed. For example,the electrolyte bath may include an alkaline solution such as PotassiumHydroxide (KOH). An electric potential is applied to the substrate whichexceeds the dielectric breakdown potential of the growing oxide layerthat grows on the substrates surface, resulting in discharges into theelectrolyte bath to create plasma reactions. For example, the substratemay be one electrode and another electrode is disposed in theelectrolyte bath. The plasma reactions modify the growing oxide layer todevelop the PEO coating. Thus, the plasma reaction may incorporateelectrolytes in the electrolytic bath into the PEO coating. For example,a PEO treatment may result in the conversion of amorphous alumina intothe harder corundum. The electrolyte material, composition of thesubstrate, and electrical potential may be influenced by the resultingthermal properties, hardness properties, strain tolerance, fatigueperformance, and adhesive properties of the desired PEO coating. The PEOcoating may be created by Keronite®.

Other exemplary, suitable methods of forming the PEO coating may besimilar to the PEO treatments described in U.S. Pat. Nos. 6,365,028 and6,896,785, and U.S. Patent Publication No. 2012/0031765, whichdescriptions are herein incorporated by reference.

Advantages of a PEO coating includes high wear resistance, hardness, andis resistant to corrosion. The PEO coating further provides a barrierbetween the substrate and wellbore fluids, such as a chemical solutionadded to the wellbore fluids. A PEO coating may grow both inward andoutward from the substrate, resulting in a coating that is well adheredto the substrate. It is believed a PEO layer is superior to aconventional anodized layer or sprayed-on hard facing due to increasedhardness caused by plasma reactions that cause the formation ofcrystalline forms of the substrate. Without being bound by theory, it isbelieved that a PEO layer provides a better fluid barrier for protectinga substrate than a conventional anodized layer or sprayed-on hard facinglayer. A PEO coating may have a relatively low coefficient of friction.However, the PEO coating is deposited on the profile elements to developan outer surface of the PEO coating that is similar (e.g., mirrors) tothe shape of the profile elements. The coated profile elements formgripping elements configured to grip the downhole surface. The grippingelements form a gripping surface of the slip.

In some embodiments, the slip body is degraded prior to the degradationof the slip insert. For example, at least a portion of the slip body130, 230 is degraded to expose a non-PEO coated surface of the slipinsert 125, 225. The exposed non-PEO coated surface of the slip insert125, 225 allows the chemical solution to cause degradation of the slipinsert 125, 225. In some embodiments, one chemical solution is used todissolve the slip body 130, 230 and a second, different chemicalsolution is used to dissolve the slip insert 125, 225.

In some embodiments, the slip segments do not include a slip insert 125,225. Instead, the slip segments are formed from a degradable material,such as aluminum or magnesium alloy, and the slip segments have profileselements, such as wickers, formed on or attached to a surface thereof.The slip segments are coated in a PEO coating. For example, the slipsegments may have a PEO coating only on the surface configured to face adownhole tubular. In some embodiments, only the profile elements arecoated. The PEO coated profile elements form gripping elementsconfigured to grip the downhole surface when the slip segments are setagainst the downhole surface. The PEO coating may reflect the shape ofthe profile elements. For example, the gripping elements may resemblewickers if the profile elements are wickers. The PEO coating isconfigured to contact and/or penetrate the downhole surface. As aresult, the slip segment with the PEO coating can be engaged with thedownhole surface to anchor the downhole tool including the slipsegments. The slip segments may include second profile elements that arecoated in a PEO coating to form teeth that are configured to engage theteeth 143 of the cone 140.

As will be understood by a person of ordinary skill in the art,conventional slips may use buttons that grip the downhole casing. Thebuttons are attached to a slip segment, and the slip segment may beformed from a dissolvable or degradable material. For example, thesebuttons may be formed from machined ductile iron, cast iron, powdermetal, ceramic, or combinations thereof. Conventional buttons aredifficult to dissolve or degrade with conventional techniques. Once theslip segments holding the buttons degrade or dissolve, the buttons areno longer held into engagement with the downhole tubular. A cleanupoperation may be necessitated to flow the buttons back to the surface.Unlike conventional buttons, the PEO coating that remains after thedegradation of the slip easily flows back to the surface or is easilyflowed downhole without the need for a time consuming cleanup operation.

In some embodiments, the PEO coatings remaining in the wellbore afterthe degradation of the downhole tool may be flowed back to the surface.In some embodiments, flowing the PEO coatings back to the surface may becompleted as part of another operation that is not dedicated to cleaningthe wellbore. Exemplary operations suitable for flowing back remainingPEO coatings include cleanup operation, a gel sweep operation, aproduction operation, or a milling operation. For example, the PEOcoating may be flowed back to the surface during an operation to degradeanother downhole tool having a PEO coating.

In some embodiment, the downhole tool 100 includes conventional buttonsas profile elements which are coated with a PEO coating. One or morechemical solutions are used to degrade the downhole tool 100, leavingthe buttons and the PEO coating. The buttons with the PEO coating may beflushed from wellbore.

In some embodiments, the PEO coating is applied to a non-degradable slipinsert. In some embodiment of the slip assembly without a slip insert,the PEO coating may be applied to a non-degradable slip body. Thenon-degradable material may be a metallic material. For example, theprofile elements may be formed from a non-degradable material, such as anon-dissolvable button. For example, a non-degradable button, such as anon-dissolvable button, may be formed from a ceramic material, powdermetal, cast iron, ductile iron, or an alloy steel. In some embodiments,the profile elements may be non-dissolvable wickers.

FIG. 6 illustrates the downhole tool 100 in FIG. 1 after activation toset the slip assembly 120 and the seal assembly 160 against a downholesurface, which is the inner surface of the downhole tubular 700. Thedownhole tubular 700 may be a casing. Before the downhole tool 100 wasactivated, the downhole tool 100 was deployed into the downhole tubular700. For example, the downhole tool 100 may be deployable downhole by awireline setting tool and the slip assembly 120 and the seal assembly160 are set by the wireline setting tool. As shown, the grippingelements 126 are engaged with the downhole surface, the downhole surfacebeing the inner surface of the downhole tubular 700. The PEO coating 129is engaged with the inner surface of the downhole tubular 700. The PEOcoating 129 may also penetrate the downhole tubular 700. Thus, the slipsegments 122 with the gripping elements 126 anchor the downhole tool 100to the downhole tubular 700 when the slip segments 122 are in theextended position. Alternative slip segments, such as slip segments 122a having slip insert 225 or a slip segment without an insert, may beused to grip the downhole tubular with corresponding gripping elementscomposed of profile elements and the PEO coating.

After the downhole tool 100 is activated, an object 200 may be droppedwhich engaged the seat 142. As shown in FIG. 6, object 200 is a ballengaged with the seat 142. The object 200 may be made of a degradablematerial, such as a dissolvable material. A fracturing operation mayoccur after the object is engaged with the seat 142. After, or during,the fracturing operation, one or more chemical solutions are introducedinto the wellbore to degrade the downhole tool 100 and/or object 200,which leave behind the PEO coating 129. The object 200 may also beextruded from the seat 142 instead of, or in addition to, beingdegraded. The PEO coating 129 may then be flowed further downhole orflowed out of the wellbore.

In some embodiments, the gripping elements 126, 226 penetrate thedownhole surface, such as the inner surface of a casing.

FIG. 7 illustrates an exemplary downhole tool 400 deployable in awellbore. The downhole tool 400 is shown disposed at the lower end of acasing string disposed in a wellbore. The downhole tool 400 includes atubular member 410 and a seat 420. The seat 420 may be made of adissolvable or degradable material. The seat 420 includes a body 422 anda PEO coating 424. The PEO coating 424 protects the body 422 of the seat420 from wellbore fluids that could damage the seat 420. For example,The PEO coating 424 protects the ball seat 420 from degradation due tofracturing fluids, such as the abrasive properties of the sand. Anobject, such as a ball, is deployable into the wellbore to engage theseat 420 (via the PEO coating 424) and closes fluid communicationthrough the seat 420. Pressure can be increased above the seated object.For example, the downhole tool 400 can be used to pressure test thecasing string.

Alternatively, the seat 420 may be incorporated into another type ofdownhole tool, such as a packer, a liner hanger, or a fracturing tool.In one embodiment, the fracturing tool may be a plug and perforationtool. For example, the seat 420 may replace seat 142, in that the seat142 of the cone 140 includes a PEO coating. In one embodiment, adownhole tool string may include a plurality of seats 420. The pluralityof seats 420 may be graduated, in that some seats 420 may have a largerdiameter than others to catch different sized objects. In someembodiments, the seat 420 is incorporated, attached to, or integral witha sliding sleeve such that pressure above an object caught by the seat420 will cause the sliding sleeve to move.

The PEO coating 424 is applied to the body 422 in substantially the sameway as described above.

FIG. 8 illustrates a downhole tool 800 used for a fracturing operation.The downhole tool includes a tubular member 810, a first sleeve 820, anda second sleeve 830. The first sleeve 820 and the second sleeve 830 aredisposed in the tubular member 810. The first sleeve 820 has a firstseat 822 coated with a PEO coating 822 c. The second sleeve 830 includesa second seat 832 coated with a PEO coating 832 c. The tubular member810 includes a first set of fracturing ports 840 and a second set offracturing ports 842. The first sleeve 820, in a first position, blocksthe first set of fracturing ports 840. The first sleeve 820 is moveableto a second position to expose the first set of fracturing ports 840 inresponse to fluid pressure above a first object, such as a ball, engagedwith the first seat 822. The second sleeve 830 is moveable to a secondposition to expose the second set of fracturing ports 842 in response tofluid pressure above a second object, such as a ball, engaged with thesecond seat 832. FIG. 8 shows the first sleeve 822 and the second sleeve832 in the second position. The second seat 832 may have a diameterlarger than a diameter of the first seat 822 such that the first objectpasses through the second seat 832 without seating against the secondseat 832. The first object may be deployed first to land in the firstseat 822 to cause the first sleeve 820 to be opened. Then, a fracturingoperation is performed to fracture the formation via the exposed firstset of fracturing ports 840. Later, the second object may be deployed toopen the second sleeve 830. Then, a subsequent fracturing operation isperformed to fracture a second zone of the formation via the exposedsecond set of fracturing ports 842. In some embodiments, one or moreshearable members may retain the first sleeve 822 and the second sleeve832 in the first position.

The PEO coating 822 c and the PEO coating 832 c protects the first seat822 and the second seat 832, respectively, from damage by wellborefluids. The protection afforded by the coatings 822 c, 832 c facilitatessealing engagement of the objects with the respective seat 822, 832 suchthat a fracturing operation can be performed. The downhole tool 800 mayinclude additional sleeves to allow additional zones of the wellbore tobe selectively fractured. The PEO coating 822 c of the first seat 822and the PEO coating 832 c of the second seat 832 may be applied insubstantially the same way as described above. In some embodiments, thedownhole tool 800 may include one or more degradable or dissolvablecomponents.

In one embodiment, a downhole tool includes a cone member and a slipassembly. The slip assembly includes a plurality of slip segments. Theslip segments are configured to move along the cone member intoengagement with a downhole surface. Each slip segment includes a slipbody, a plurality of degradable profile elements coupled to the slipbody, and a first coating disposed on the plurality of profile elements,wherein the first coating is formed from a plasma electrolytic oxidationtreatment. The first coating and profile elements form a plurality ofgripping elements configured to grip the downhole tubular.

In some embodiments of the downhole tool, the slip body is formed from adegradable material.

In some embodiments of the downhole tool, the slip body has a pluralityof teeth disposed on a surface opposite of the plurality of profileelements, and wherein the plurality of teeth are configured to engagewith a plurality of teeth of the cone member.

In some embodiments of the downhole tool, the slip body further includesa pocket and a slip insert disposed in the pocket, wherein the slipinsert includes the gripping elements.

In some embodiments of the downhole tool, wherein the slip body isformed from a degradable polymer and the slip insert is formed fromeither an aluminum or magnesium alloy.

In some embodiments of the downhole tool, wherein the slip insert has alower surface opposite the engagement surface, the lower surfaceincluding a plurality of teeth configured to engage with a plurality ofteeth of the cone member, wherein the teeth of the slip insert arecomposed of a plurality of second profile elements with a second coatingdisposed thereon, wherein the second coating formed from the plasmaelectrolytic oxidation treatment and.

In some embodiments of the downhole tool, the profile elements arewickers.

In some embodiments of the downhole tool, the profile elements areattached to the slip insert.

In some embodiments of the downhole tool, the profile elements areformed from a magnesium alloy.

In one embodiment, a downhole tool includes a slip assembly having aplurality of slips configured to engage a downhole surface. The slipassembly includes a plurality of slip segments. Each slip segmentincludes a slip body, a plurality of profile elements coupled to theslip body, and a first coating disposed on the plurality of profileelements, wherein the first coating is formed from a plasma electrolyticoxidation treatment. The first coating and the plurality of profileelements form a plurality of gripping elements configured to grip thedownhole surface.

In some embodiments of the downhole tool, the slip body is formed from adegradable material.

In some embodiments of the downhole tool, the slip body further includesa pocket and a slip insert disposed in the pocket, wherein the slipinsert includes the plurality of gripping elements.

In some embodiments of the downhole tool, the slip body is formed from adegradable polymer and the slip insert is formed from either an aluminumor magnesium alloy.

In some embodiments of the downhole tool, wherein the slip insert has alower surface opposite the engagement surface, the lower surfaceincluding a plurality of teeth configured to engage with a plurality ofteeth of a cone member, wherein the teeth of the slip insert arecomposed of a plurality of second profile elements with a second coatingdisposed thereon, wherein the second coating formed from the plasmaelectrolytic oxidation treatment and.

In some embodiments of the downhole tool, the profile elements areattached to the slip insert.

In some embodiments of the downhole tool, the profile elements areformed from a degradable material.

In some embodiments of the downhole tool, the profile elements areformed from a magnesium alloy.

In some embodiments of the downhole tool, the profile elements are aplurality of non-dissolvable buttons.

In one embodiment, a method of using a downhole tool includes deployinga downhole tool into a downhole tubular. The downhole tool includes aslip assembly. The slip assembly includes a plurality of slip segmentshaving a coating formed from a plasma electrolytic oxidation treatment,wherein the coating is configured to grip the downhole tubular. Themethod further includes activating the downhole tool to engage theplurality of slip segments with the downhole tubular, wherein thecoating grips the downhole tubular such that the slip assembly anchorsthe downhole tool to the downhole tubular.

In some embodiments, the method further includes performing a fracturingoperation with the downhole tool.

In some embodiments, the method further includes suppling one or morechemical solutions downhole to degrade the downhole tool, wherein thecoating is left in a wellbore upon the degradation of the downhole tool.

In some embodiments, the method further includes flowing the coating tothe surface.

In some embodiments of the method, the slip insert includes the coating.

In one embodiment, a downhole tool includes a tubular member and a seathaving a coating, wherein the coating is formed from a plasmaelectrolytic oxidation treatment.

In some embodiments of the downhole tool, a sleeve disposed in thetubular member includes the seat, wherein the sleeve is moveable from afirst position to a second position in response to a fluid pressureabove an object engaged with the coating.

In one embodiment, a downhole tool includes a slip assembly having aplurality of slips configured to engage a downhole surface. The slipassembly includes a plurality of slip segments. Each slip segmentincludes a slip body, a plurality of degradable profile elements coupledto the slip body, and a first coating disposed on the plurality ofprofile elements, wherein the first coating is formed from a plasmaelectrolytic oxidation treatment. The first coating and the plurality ofprofile elements form a plurality of gripping elements configured togrip the downhole surface.

In some embodiments of the downhole tool, the slip body is formed from adegradable material.

In some embodiments of the downhole tool, the slip body further includesa pocket and a slip insert disposed in the pocket, wherein the slipinsert includes the plurality of gripping elements.

In some embodiments of the downhole tool, the slip body is formed from adegradable polymer and the slip insert is formed from either an aluminumor magnesium alloy.

In some embodiments of the downhole tool, wherein the slip insert has alower surface opposite the engagement surface, the lower surfaceincluding a plurality of teeth configured to engage with a plurality ofteeth of a cone member, wherein the teeth of the slip insert arecomposed of a plurality of second profile elements with a second coatingdisposed thereon, wherein the second coating formed from the plasmaelectrolytic oxidation treatment and.

In some embodiments of the downhole tool, the profile elements areattached to the slip insert.

In some embodiments of the downhole tool, the profile elements areformed from a magnesium alloy.

In one embodiment, a downhole tool includes a tubular member and a seatincluding a coating. The coating is formed from a plasma electrolyticoxidation treatment.

In some embodiments of the downhole tool, a sleeve disposed in thetubular member includes the seat, wherein the sleeve is moveable from afirst position to a second position in response to a fluid pressureabove an object engaged with the coating.

While the foregoing is directed to embodiments of the presentdisclosure, other and further embodiments of the disclosure may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims that follow.

What is claimed is:
 1. A downhole tool, comprising: a cone member; and aslip assembly having a plurality of slip segments, the slip segmentsconfigured to move along the cone member into engagement with a downholesurface, wherein each slip segment includes: a slip body; a plurality ofdegradable profile elements coupled to the slip body; and a firstcoating disposed on the plurality of profile elements, wherein the firstcoating is formed from a plasma electrolytic oxidation treatment;wherein the first coating and profile elements form a plurality ofgripping elements configured to grip the downhole tubular.
 2. Thedownhole tool of claim 1, wherein the slip body has a plurality of teethdisposed on a surface opposite of the plurality of profile elements,wherein the plurality of teeth are configured to engage with a pluralityof teeth of the cone member.
 3. The downhole tool of claim 1, whereinthe slip body further includes: a pocket; a slip insert disposed in thepocket, wherein the slip insert includes the gripping elements.
 4. Thedownhole tool of claim 3, wherein the slip body is formed from adegradable polymer and the slip insert is formed from either an aluminumor magnesium alloy.
 5. The downhole tool of claim 3, wherein the slipinsert has a lower surface opposite the engagement surface, the lowersurface including a plurality of teeth configured to engage with aplurality of teeth of the cone member, wherein the teeth of the slipinsert are composed of a plurality of second profile elements with asecond coating disposed thereon, wherein the second coating formed fromthe plasma electrolytic oxidation treatment and.
 6. The downhole tool ofclaim 3, wherein the profile elements are wickers.
 7. The downhole toolof claim 3, wherein the profile elements are attached to the slipinsert.
 8. The downhole tool of claim 1, wherein the profile elementsare formed from a magnesium alloy.
 9. A downhole tool, comprising: aslip assembly having a plurality of slips configured to engage adownhole surface, the slip assembly including: a plurality of slipsegments, wherein each slip segment includes: a slip body; a pluralityof profile elements coupled to the slip body; and a first coatingdisposed on the plurality of profile elements, wherein the first coatingis formed from a plasma electrolytic oxidation treatment; wherein thefirst coating and the plurality of profile elements form a plurality ofgripping elements configured to grip the downhole surface.
 10. Thedownhole tool of claim 9, wherein the slip body is formed from adegradable material.
 11. The downhole tool of claim 9, wherein the slipbody further includes: a pocket; a slip insert disposed in the pocket,wherein the slip insert includes the plurality of gripping elements. 12.The downhole tool of claim 11, wherein the slip body is formed from adegradable polymer and the slip insert is formed from either an aluminumor magnesium alloy.
 13. The downhole tool of claim 11, wherein the slipinsert has a lower surface opposite the engagement surface, the lowersurface including a plurality of teeth configured to engage with aplurality of teeth of a cone member, wherein the teeth of the slipinsert are composed of a plurality of second profile elements with asecond coating disposed thereon, wherein the second coating formed fromthe plasma electrolytic oxidation treatment and.
 14. The downhole toolof claim 9, wherein the profile elements are formed from a degradablematerial.
 15. The downhole tool of claim 9, wherein the profile elementsare a plurality of non-dissolvable buttons.
 16. A method of using adownhole tool, comprising: deploying a downhole tool into a downholetubular, the downhole tool including a slip assembly, the slip assemblyincluding: a plurality of slip segments having a coating formed from aplasma electrolytic oxidation treatment, the coating configured to gripthe downhole tubular; and activating the downhole tool to engage theplurality of slip segments with the downhole tubular, wherein thecoating grips the downhole tubular such that the slip assembly anchorsthe downhole tool to the downhole tubular.
 17. The method of claim 16,further comprising: performing a fracturing operation with the downholetool.
 18. The method of claim 17, further comprising: suppling one ormore chemical solutions downhole to degrade the downhole tool, whereinthe coating is left in a wellbore upon the degradation of the downholetool.
 19. The method of claim 18, further comprising: flowing thecoating to the surface.
 20. The method of claim 18, wherein the slipsegments include a slip insert, wherein the slip insert includes thecoating.